OBD-II code · Powertrain (generic, extended)
P21F9 Fuel Control System B Too Rich at Idle (Bank 1)
Fuel Control System B Too Rich at Idle (Bank 1): the fuel-trim control is correcting for an over-rich mixture in this operating range.
Is it safe to drive with P21F9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyInjectors leak at low duty cycle
Symptoms
- Check engine light on
- Increased fuel consumption
- Black smoke from exhaust on acceleration
- Smell of unburned fuel, fouled spark plugs
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.7–4 h
- Emissions test
- Likely to fail
- Parts involved
- Fuel Injector, Fuel Pressure Regulator
Related codes
- P21F5Fuel Control System B Too Rich Off Idle (Bank 1)
- P21FBFuel Control System B Too Rich at Idle (Bank 2)
- P21F6Fuel Control System B Too Lean Off Idle (Bank 2)
- P21F7Fuel Control System B Too Rich Off Idle (Bank 2)
- P21F8Fuel Control System B Too Lean at Idle (Bank 1)
- P21FAFuel Control System B Too Lean at Idle (Bank 2)
- P21FCFuel Control System B Too Lean at Higher Load (Bank 1)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.